Fire development in focus

This article appeared in the Spring 2012 edition of Fire Australia magazine.

Large bushfires can be destructive, but how do they progress to this state? A team of Bushfire CRC researchers is investigating how bushfires develop. By Nathan Maddock, Fire Australia magazine Joint Editor.

All bushfires start small, but how do they progress to large fires that can impact on communities and cause wide-scale destruction? Until now, our existing knowledge of fire behaviour and tools for prediction assumed steady-state spread of a fire. Understanding the chances of a fire occurring and developing into a large fire, as well as the likelihood of spot fires, is essential to understanding the behaviour of bushfires under all possible weather conditions. This is exactly what a team of Bushfire CRC researchers is looking at.

Three key aspects are being investigated: the potential for a fire to start; the potential for a fire to develop beyond initial attack; and once a fire starts spotting, when these spot fires will be beyond initial attack.

Understanding these important phases of fire development will help clarify resource demands placed on fire brigades, provide greater confidence in preseason planning and assist in issuing public warnings.

Dr Andrew Sullivan is the Bushfire CRC’s research leader for the project and a Senior Research Scientist at the CSIRO. He said the team is looking at the problem from a number of different perspectives, which hasn’t been done in the past.

“We are taking a multi-pronged approach to the research,” he said.

“We’re considering a large number of experimental fires that were conducted in the 1950s and 1960s by Alan McArthur and his associates. These fires were lit at one particular point and then studied for a period of time, sometimes minutes, sometimes up to an hour, before they were extinguished.”

In conjunction with the historical data, the team is conducting tests of its own using the CSIRO pyrotron. The pyrotron is a horizontal wind tunnel that allows fires to be studied under repeatable conditions in safety.

“We cannot control all the variables in field research,” said Dr Sullivan.

“It’s also very hard to be in the right place at the right time to make observations. “We’re looking at the rate of growth of fires that are at different sizes when ignited,” Dr Sullivan added.

Dr Sullivan noted that the McArthur experiments have played an important part in fire science, science that is still used today.

“The experimental fires conducted in the past have been instrumental in the development of the current McArthur fire danger rating systems for forests and grasslands,” he said.

In addition to developing the fire danger rating systems, vast amounts of data collected during McArthur’s experimental fires weren’t used. Dr Sullivan and his team will also be using these data.

“The rate of growth, which is how fast a fire will develop from a point ignition to a fire that is burning at its steady-state, wasn’t analysed in the past.”

Point ignition refers to fires that start at one point, such as from a lightning strike or from a match. This is distinct from fires that may have been burning for some time, or lit in a line, such as prescribed fires. This also includes spot fires, as Dr Sullivan explained.

“Spot fires are fires that have been started during a bushfire by firebrands carried ahead of the main fire.”

A firebrand can be any type of fuel that becomes airborne while still burning, such as twigs or bark.

“Spotting is one of those aspects of bushfire behaviour that’s been recognised for many years, and has been investigated a number of times, but is so complex.”

Spotting behaviour can fluctuate in response to variations in fuel, topography and weather, and interactions with the atmosphere. The three aspects of the project come together to help predict the spread of a fire.

“We want to be able to provide fire authorities with better information on the potential of a fire to be beyond initial attack by the time the first fire crew gets to the site.

“If a fire is beyond the first crew’s control, then fire authorities need to move to the next phase of suppression,” said Dr Sullivan.

Simon Heemstra, Manager of Community Planning at the New South Wales Rural Fire Service (RFS), is the lead end user for this project. He believes the project has the potential to fill one of the major gaps in fire behaviour prediction.

“The implications for both the RFS and firefighting agencies in general are significant,” he said.

“A greater understanding of fire growth during the initial development of a fire has the potential to increase the accuracy of fire-spread predictions. This will help with protecting and warning communities, as it will increase the accuracy of the predictions of what time a fire may impact.

“The project also has the potential to increase suppression efficiency, and in turn assist in better resource allocation, which may enable fires to be contained faster, increasing the number of fires that can be contained on days when there are many fires occurring.”

The outcome of the research project will be new knowledge on fire behaviour—knowledge that can be incorporated into existing fire behaviour modelling systems or used to improve planning for prescribed burning operations.

This will provide support for fire managers’ evolving decision needs, including community warnings, planning, operations, monitoring and assessment.